So I drove my S13 SR20'd S14 to Orlando and back this weekend. The car drove awesome the entire way there. Good gas mileage, ran like a champ. New motor works great. No smoking, ran absolutely perfectly.

THEN. I start it up this morning to come into work, and it starts hesitating on partial throttle. Pulls like it should when it's on boost, and it feels fine while accelerating, but while crusing its bucking and shaking pretty badly. It also doesn't want to idle, but only sometimes. Some of the lights I stopped at it was pulling ~16-18 in/hg of vaccum at 1000rpm, but at other lights I was pulling 5 in/hg and it was trying to shut off (like 500rpm). Really odd.

Any suggestions of what I should check? Did a quick look around the engine bay, and all my t-bolt clamps seem tight on the couplers, and there's no obvious boost leaks, but that's sorta what it feels like. Except it runs great under acceleration... Someone help!

 

Part throttle hesitation and shaking sounds like a lean condition.

It's probably a vacuum leak on/around the intake manifold. Something small will lean it way out at idle/cruise where you're not using a bunch of air. Under boost, the effect would be much smaller which is probably why it seems normal.

 

intake manifold gasket leaking? it was in rough shape when I swapped out the longblock last week, so i just used gray rtv to seal it up. lol, I know... and I kinda think that might be the issue. does sentra sr20 intake manifold gasket work?

its just odd that it ran perfectly all weekend, driving it on the highway, around orlando, partial throttle, full throttle. then almost immediately this morning when I started driving it was hesitating and idling poorly... ranlet and i are gonna try and find vacuum leaks tonight.

would bad coolant temp sensor or bad maf cause issues like this?

 

Well I was thinking just vac leak in general, which would include hoses. Your gasket is probably fine.

But I have another obscure, better fit scenario (I feel like Dr. House)....

You have a vented BOV and it's sticking. That is why it'll still idle fine sometimes (not stuck), why it's lean (stuck open, sucking around mafs), and why it's fine under boost (being forced shut). Get it to idle shitty, then cap your hand over the bov.

As far as CTS or MAFs, the CTS will just make it run really rich. The MAFs could be reading lean, but you usually get a failure and a 2500rpm limit. I've seen bad O2's force the ECU to self-learn into obivion (lean), but I think that was just a ROM tuning test gone wrong.

 

a coolant temp sensor did similar things to my old CA18.

 

no bov. so, nope on that idea. and all hoses are new on/around manifold. so I don't think they're leaking, but maybe. I'll try spraying carb cleaner on everything to test for leaks.

mattback presented another idea. possible bad ground wire to maf? working, then not working?

also gonna try unplugging my o2 sensor on the way to lunch, matt says it might cause some of these issues. he's gonna take a look at it at lunch.

 

well, with unplugged o2 sensor car seems to run fine again... I have a skinny redtop o2 sensor on a blacktop s13 ecu. Which apparently doesn't work too well. Lol.

I'll update tonight after we test for leaks.

 

spark plugs gapped too big? my old sr did that

 

Well there you go. O2 causing self-learn to go off into oblivion. But yeah, check your grounds on the back of the intake manifold, while you're poking around.

 

I had this problem before. Similar problem occurred. tightened them down and fixed.